The "information explosion" which has inundated the modern world has resulted in the necessity of providing compact methods of information storage. Although miniaturized photo reproduction techniques such as microfilm and microfiche have wide spread uses for archival storage, the temporary and re-usable storage utilizations have been taken over almost entirely by magnetic storage media. The magnetic media include tapes, disks, drums, cards and badges. The information is recorded on the media by altering the direction of magnetization of the ferrimagnetic or ferromagnetic coatings on the medium surface.
Data ordinarily recorded on magnetic media, and particularly upon magnetic disks, is required to be accurate. Modern computer and data processing systems require accurate retrieval of information from the disks in order to function properly. A small error in the retrieval of data may lead to a multiplicity of major errors in the finished result.
Consequently, it is necessary to test recording media and data transfer equipment to eliminate errors resulting from faulty data storage or a retrieval. Various techniques, methods and devices have been developed to test magnetic media for errors.
One method of testing magnetic tape for data omissions or "drop-outs" is disclosed in U.S. Pat. No. 3,525,930, issued to F. J. Hodge. This patent discloses a device designed to test magnetic tapes for drop-outs. This sort of device is known as a tape certifier. Another tape certifying device is disclosed in U.S. Pat. No. 3,947,875, issued to F. W. Bull et al. The tape test device disclosed by Bull relates to a spiral track testing apparatus which tests for drop-outs as well as many other characteristics.
Drop-out testing methods specifically related to magnetic disks are described in U.S. Pat. No. 3,781,835, issued to C. N. Dion et al. and in U.S. Pat. No. 3,686,682, issued to M. I. Behr et al. Both of these patents disclosed test apparatus for certifying magnetic disks as well as methods of utilizing the apparati. Both the Behr and Dion methods contemplate utilizing a portion of the test apparatus to record specified signals on the recording medium and then immediately reading those signals to test whether the medium has properly accepted the data. In this manner, the drop-out points on the medium may be recognized.
However, no adequate safeguards are provided against failures in the certification devices as opposed to those in the recording medium. There is no presently utilized method of adequately certifying the certifiers.